20 Mr. E. G. Young. On the Optical Rotatory 



To eliminate the possible errors due to the presence of proteins and salts, 

 the method of dilution was adopted. Thus, 1 c.c. of fluid was pipetted into a 

 test-tube, 4 c.c. of water (CCVfree) added, and a suitable quantity of the 

 indicator. A comparator was employed in the case of any turbidity or 

 foreign coloration. This method of dilution was later verified by the use of 

 the hydrogen electrode and potentiometer, and found to give correct values. 

 The values obtained with the above indicators were also verified by the 

 electrical method on test solutions. Methyl red, neutral red and phenol 

 phthalein give very trustworthy figures. 



Experiment 1. — A concentrated solution was quickly prepared from freshly 

 crystallised material, filtered and placed in a 400-mm. tube. Its rotation was 

 observed at intervals in a polarimeter for several clays and found to remain 

 absolutely constant from the first observation of — 15 - 35°. The Pn of this 

 solution was found to be 4'9. To this solution was added normal H2SO4 until 

 the acidity was increased to Pn 3"75. Within a few minutes a very finely 

 divided precipitate began to form which remained suspended and could be 

 neither filtered nor centrifuged off. Further addition of acid so that the 

 Pn became 2*7 merely increased the fine insoluble precipitate. A slow denatu- 

 ration was apparently taking place and the solution was extremely sensitive 

 to mechanical shock, immediately formiug films of denatured material. 



Experiment 2. — A fresh solution of Vn 4'9 was made alkaline by the 

 addition of several drops of concentrated NaOH solution and the variation 

 in the degree of rotation observed in a 200-mm. tube is recorded in 

 Table IV :— 



Table IV. 



Date. 



Temperature. 



Ph. 



OE. 





C. 



11 -o 



4-9 



-1 -91 



„ 13 



11 -o 



4-9 



-1-91 



» 15 



11 -o 



4-9 



-1 91 



15 



11 -o 



6 -65 



-1 -72 



„ 16 



11 -5 



6 65 



-1-73 



» 19 



12 "0 



8-4 



-1 -78 



„ 20 



12 -0 



8-4 



-1-79 



>, 21 



12 -0 



8-4 



-1-80 









A distinct though small drop in rotatory power was observed and on 

 further increasing the hydroxyl ion concentration the value for the rotation 

 increased slowly. 



The effect of adding concentrated NH 4 OH to a fresh solution of albumin 

 was next tried, employing a higher concentration of protein. Precisely the 



